Duplexer



M. GARDEN Oct. 22, 1957 DUPLEXER Filed Oct. 23. 1955 liu-- NNI. 4.

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States DUPLEXER Murray Garden, Haddonfield, N. J., assigner to RadioCorporation of America, a corporation of Delaware The present inventionis related to duplexers, and particularly to duplexers operative in themicrowave frequency region.

Microwave dupiexers are well known. Their function may be described inconnection with pulsed radar (radio echo detection and ranging) systems.In these systems, a microwave generator transmits pulses of radiofrequency energy under control of a pulse modulator. The energy isapplied to an antenna through a transmission line. At a branch point thetransmission line leads to a receiver. The duplexer may include a TR(transmitreceive) and ATR (anti-transmit-receive) arrangement. Theseoperate to connect the antenna to the generator under transmitconditions and disconnect the receiver. Under non-transmit conditions,the duplexer connects the antenna to the receiver and disconnects itfrom the transmitter. This function may be performed by a simple TRswitch positioned at the proper distance from the branch point towardthe receiver, and the branch point must be properly positioned.Additionally, an ATR (antitransmit-receive) switch may be inserted inthe transmission line between the transmitter or microwave generator andthe branch point. When an ATR switch is used, the branch point positionin relation to the generator (excluding the ATR) is not so important. Athigh power levels, it is sometimes useful to use a pre-TR switch or tubewhich aids the TR switch in reiiecting energy which might otherwise passto the receiver.

The various switches employed as TR, ATR, and pre- TR switches usuallytake the form of a resonant circuit coupled with a gas discharge tube.Sometimes, these components may be used interchangeably, that is, acomponent which in one case serves as a TR tube may in another caseserve as a pre-TR tube. However, it is not convenient to employ TRswitches which are designed for use with hollow pipe waveguide withcoaxial line waveguide. On the other hand, it is sometimes inconvenientto use hollow pipe waveguide, because such waveguide is too bulky at thedesign frequency for the proposed use. Coaxial line is more compact, butdoes not have the power carrying capacity. However, if standard coaxialline waveguides are to be employed at microwave frequencies with TRcomponents commercially available and of the type suited for hollow pipewaveguide, then a transition must be designed in order to enable the useof the standard component. Such transitions usually are space consuming.On the other hand, coaxial line pre-TR tubes are not available.Therefore, under certain design requirements, it becomes desirable toemploy the hollow pipe waveguide pre-TR tube and other TR componentswith a coaxial line system.

it is an object of the present invention to provide a TR arrangementwhich is compact and uses standard hollow pipe waveguide components inconjunction with coaxialline waveguide.

Another object of the invention is to Vprovide a TR, pre-TR arrangementemploying hollow pipe waveguide components but associated with coaxialline waveguide.

arent @i A further object of the invention is to employ hollow pipewaveguide TR components in conjunction with coaxial line waveguide witha saving of space and a compact arrangement.

In accordance with the invention, at the junction between the receivertransmission line and the coaxial transmission line from transmitter toantenna, a compact transition section from coaxial line to hollow pipewaveguide is inserted. At this junction point, a pre-TR switch isinserted. Notwithstanding that the compact pre-TR arrangement and itstransition is mismatched at the high microwave frequency at which it isto operate, a TR cavity arrangement interposed close to the pre-TRswitch in the line to the receiver is tuned in such a way that theentire circuit is resonant at the desired operating frequency, and themismatch of the preTR switch is tuned out by the TR cavity tuning,

The foregoing and other objects, advantages and novel features of theinvention will be more fully apparent from the following descriptionwhen taken in connection with the accompanying drawing, in which likereference numerals refer to like similar parts, and in which The solefigure is a diagram, schematically portraying a radar system in whichthe invention may be embodied, and showing in cross-section the TR andpre-TR arrangement according to the invention.

Referring to the drawing, the transmitter mayinclude a magnetrontransmitter 16 under control of a pulse modulator 12. The transmitterlil is connected to apply energy through an ATR switch le and atransmission line i6 to an antenna 13 which may have directionalcharacteristics and be directed as desired. The transmission line 16 isa coaxial transmission line or coaxial waveguide. it must handlesubstantial amounts of power, but conservation of space is in thisinstance very important. The pre-TR, TR arrangement 20 includes a TRswitch 22 and a pre-TR switch 24 coupledby a short section ofrectangular hollow pipe waveguide 26. The junction A between the pre-TR,TR arrangement 2@ and the coaxial waveguide 16 is made by a transition28 from coaxial line to hollow pipe waveguide. The hollow cavityresonator 30 of the TR switch 22 is coupled to the receiver 32 by acoupling loop 34 through a coaxial line.

The operation of the system as a whole may be understood from theforegoing. The general operation of such systems is well explained inRadar System Engineering edited by Ridenour, vol. 1 of theV RadiationLaboratory Series published by McGraw-Hill section 11.5, page 407.Reference may also be made to Microwave Receivers edited by Van Voorhis,vol. 23 of the Radiation Laboratory Series, chapter 2 beginning at page7. When the magnetron il) transmits under control of the pulse modulator12, the ATR, pre-TR, and TR switches are tired. The transmitter 10 isthen connected to the antenna. The branch line to the receiver 32 isblocked because of the short circuit eifectively across this branch linebecause of the ring of the TR and pre- TR switches. The energy thereforepasses to the antenna, and is prevented from passing to the receiver.

The ATR switch ie in this particular equipment is effectively in serieswith the coaxial waveguide 16, and is spaced effectively three quarterswavelength from the junction A. Therefore, when the magnetron ortransmitter 10 is in the non-transmit condition under control of thepulse modulator 12, energy from the antenna 18 passing along the coaxialwaveguide 16 is blocked at the junction A looking in the direction ofthe magnetron 10. In the direction of the receiver, however, neither thepre-TR switch 24 nor the TR switch 22 is tired, and energy passes to thereceiver as though the coupling were direct, and the pre-TR and TRarrangement 2t) were not interposedr The function of the pre-TR switch24 is readily .explained in thatwhen there. shigh Vpowered transmissionthe TR switch alone and by itself is insufficient to prevent damage tothe receiver. Accordingly,

it i'soften desirable lto inserta pre-TRswitch';V VThis pre-V halfportion on; one side of a radial planethrough the axi'sofithe' coaxialline;A Thus,V as viewedl in the figure, the enlargement .is made. .inthe upper portion of the outerxlconductoraof .the coaxial line 16. Theenlarged portionthus has side walls. 36 and continuity with theremaind'erof the outery conductor ismaintained byY including-partial.bottomfwalls 3S to completethe section 26 of rectangular hollow pipeVwaveguide, the longitudinal axismof. which is.Y at right angles Vto thelongitudinal axis othecoaxial waveguide 16, and having an end opening.contiguous withhalf. of'a cylinder formed by the outer conductor. .ofline 16.V The -inner conductor 40 of the coaxialiwvaveguide 16 mayalsosbe enlarged at the point Where .the `outerlconductor is enlarged toimprove the shofwnlto holdftheportion 54 in place. A pair of metalgaskets 46, and 48 are provided which grasp between them :the metal.platee' of the pre-TR switch 24. A pre-TR ltube 52 is mounted in aresonant aperture in the plate S0. -The 'hollow pipe waveguide section26Y formed by the .rectangular sidewalls S6-is continued by the gaskets46 vand48 and by wthefurther portion-54 until it merges into acavityresonator V56. The cavity resonator 56 is part of `the TR switch22whichincludes the TR tube 58. The TR ytube' -ism'ountedinia standardfashionand `has a tuning .mechanism actuated by rotation of a shaft` 60.It is .contemplated that 4thershaft 60 may be remotely adjustedsbygmeaus ofa llexible rotatable shaft. As understood `in fthe art,'tlie.shaft `60controlsthe spacing of-a pair fof keepaliye-.electrodeswithin the tube which in turn vary thetiresonant frequency .of thecavity resonator 56. The` TR- tubef is a standardl type modified byremoving its tuning knob and mechanically coupling the rotatableshaftltortheiknob shaft. The-couplingloopi is lo- ;catedi-on theside ofthe cavity resonator 56 remote from vthe side into .which thewaveguidesection 54 leads.

The coupling loop '34 leads toa coaxial transmission line 62.'which'make'siaright. angle Yturn at Y64 and leadsrto Ya crystalinserted in the transmission line at 66. Only the crystallcartridge 68is shown, thecrystal and its contact .-Within the holder V(not shown)being Vwell. known in the The coaxialtransmission line 62 has an innerconductor 80.- The inner conductor 84 of a section of coaxialtranscoupling VVdisc of 'couplingSZ in relationtoJthe inner conductor S0may be varied by a nut V88 and locked in place by a c ooperating locknut 90. .The coaxialltransymission line 86 leads/to an ordinary typecaf-coaxialV line jconnector 92 for ready connection to a localoscillator (not shown). Y

In operation, itis well to bear in mindthat the oper- Vating frequencymay be 1300 mc. (megacycles per second) 'Becauseof the high transmittedVpower in this system, it is Yessential that a pre-TR switch beiemployed.Such a great amount of energy is'fed through to the receiver duringtransmit periods, if only a TR switch is employed,

zandwith the plate 50provides a substantiallycontinuou's Y -apertureinwhich is located a low'pressure gasftube,

5. that damage to the receiver, e. g., crystal 'burnout,` results. Atthe f requency of operation, however, a pre-,TR tube or pre-TR switch isavailable as a standard component only for hollow pipe waveguide.Moreover, to design a pre-TR tube for coaxial waveguide would requirenot only considerable engineering skill but would be very'ditficult.However, using the transition section made byenlarging theout'er.conductor of the coaxial line 16 into a rectangular hollowtpipewaveguide section with sidewalls 36, the standard hollow pipe waveguide1 pre-TR tube 52and1thestandard switch 24 may be insertedV into thissection of rectangular hollow pipe vwaveguide, which is then continuedYinto the waveguide section 26. Y Unfortunately, this coupling ortransition Section 28 does not provide ajgood, match at the operatingfrequency, during reception, Notwithstanding, a match at the operatingfrequency during reception may be secured by suitably tuning the tube58. In transmission, a good receiver protection is. secured by spacingthe pre-TR and TR tube theoretically a quarter-wavelength. ln practice,Y

the spacing is made slightly different, in. this case less than aquarter wavelength, in order to secure good results `with .a.matcheducondition during reception. This departure from aquarterwavelength did Vnot causerexcessive leakage to the receiver duringtransmission. Although the transition 28 into the rectangular waveguideprovides Aonly. a poormatch Ato the receiver through the pre-TRresonant.aperture, the tuning of the TR cavity andthe properspacing'comp'en'sate for the transition Ymis-match, and the unit as awhole give proper and highly desirable operation. The unit 2 0is, infact, much morek compact .than many. other'. systems which are providedwith Va proper .matching section for the'transition selected from.amongthosewhichg are known.

During ,transmit .conditions the pre-TRtube 52 is tired end wall tojthe.enlarged rectangular cavity transition 28.

-Feed throughto, the crystalis further prevented by theV tiringofithecavity'resonator tube V58 inthe cavity resona- -tor 56.

` The following y tube VVtypes may be employed: For the pre- TRgtube52,Vv a type WL6260; for the TR tube 58, altype BL25.'v Although the ATRtube is not. shown in (detail it may be anarrangement similar to thatillustrated in Fig. 2.5 0a of section 2.10 of chaper 2 of MicrowaveDuplexers. .edited jby. Smullingand Montgomery, vol. 14 VoftheRadiationLaboratory Series, and also employing a type .BL25 TR tube.

In view of the foregoing, it'will bev apparent that'the `invention`provides .an especially compact pre-TR and TR Varrangement fofmicrowave frequencies for high power transmission. .outerYconductrftransition section of coaxial line leading into ashort sectionof -hollowpipe waveguide in which is inserted a preTR;t`ube in the formof a plate obstructing thewaveguidetransit'ion. section `but having aresonant Y outer conductor havinga portion thereof expanded and jenlarged intotka rectangular hollow pipe waveguide section, anda'transit-r'eceive switchv at the termination of A lsaid hollowpipeVwaveguide section remote fromsaid outer yconductor and coupled thereto,f a YAY.pre-'transmit-receive `switchin'said'hollowpiper'waveguidesection spaced an Y odd multiple, including unity,'"of quarter"wavelengths The Varrangement includes. an enlargedV from saidtransmit-receive switch, said hollow pipe waveguide section andpre-transmit-receive switch being mismatched to said coaxial linesection at the operating frequency, said transmit-receive switch beingtuned to compensate for said mismatch.

2. A transmitreceive arrangement comprising a coaxial line waveguidesection having an inner conductor and an outer conductor, a section ofhollow pipe waveguide, and a cavity resonator, said hollow pipewaveguide section having one end coupied to said coaxial line waveguidethrough an enlarged outer conductor portion thereof, and the other endcoupled to said cavity resonator, said hollow pipe waveguide having atsaid one end a pre-trausmit-receive switch spaced an odd multiple,including unity, of quarter wavelengths from said cavity resonator, saidtransition and said pre-transmit-receive being mismatched at theoperating frequency, said cavity resonator being tuned to compensate forsaid mismatch and to match said transition section and saidpre-transmit-receive together with said resonator at said operatingfrequency.

3. The transmit-receive arrangement claimed in claim 2, saidpre-transmit-receive switch comprising a metallic plate obstructing saidhollow pipe waveguide, and having a resonant aperture with a lowpressure gas tube mounted in said aperture.

4. The transmit-receive arrangement claimed in claim 2, said innerconductor having a portion of radius enlarged over the radius ofadjacent portions thereof, said enlarged radius portion beingsubstantially coextensive along the length of the line with saidenlarged outer conductor portion.

5. The transmit-receive arrangement claimed in claim 2, the coupling ofsaid hollow pipe waveguide section to said cavity resonator comprisingthe termination of said section in an opening communicating directlywith the resonant cavity of said resonator.

6. The transmit-receive arrangement claimed in claim 5, said innerconductor having a portion of radius enlarged over the radius ofadjacent portions thereof, said enlarged portion being substantiallycoextensive along the length of said coaxial waveguide with saidenlarged outer conductor portion.

7. A transmit-receive arrangement comprising a coaxial line waveguidefor connecting a transmitter and an antenna and having an innerconductor and an outer conductor, a hollow pipe waveguide branching fromsaid coaxial line waveguide outer conductor at a junction, apre-transmitrece1ve switch in said hollow pipe waveguide at saidjunction, a transmit-receive switch in said hollow pipe waveguide remotefrom said junction, said pre-transmit-receive switch alone beingmismatched at the operating frequency, said transmit-receive switchbeing tuned to compensate for said mismatch, a further waveguide forconnection to a receiver, said further waveguide by the tuning beingcoupled with a matched coupling at the operating frequency to saidcoaxial line waveguide by said hollow pipe waveguide during non-transmitperiods of the transmitter.

8. The transmit-receive arrangement claimed in claim 7, saidtransmit-receive and said pre-transmit-receive switches being spacedapart slightly less than one quarter wavelength measured at saidoperating frequency.

References Cited in the le of this patent UNITED STATES PATENTS

